// JavaScript Document
function checkForm()
{
   // the variables below are assigned to each
   // form input
   var gname, gemail, gurl, gmessage;

   with(window.document.guestform)
   {
      gname    = author;
      gemail   = email;
      gurl     = url;
      gmessage = comment;
   }

   // if name is empty alert the visitor
   if(trim(gname.value) == '')
   {
      alert('Please enter your name');
      gname.focus();
      return false;
   }
   // alert the visitor if email is empty or
   // if the format is not correct
   else if(trim(gemail.value) != '' && !isEmail(trim(gemail.value)))
   {
      alert('Please enter a valid email address or leave it blank');
      gemail.focus();
      return false;
   }
   // alert the visitor if message is empty
   else if(trim(gmessage.value) == '')
   {
      alert('Please enter your message');
      gmessage.focus();
      return false;
   }
   else
   {
      // when all input are correct
      // return true so the form will submit
      return true;
   }
}
/*
Strip whitespace from the beginning and end of a string
*/
function trim(str)
{
   return str.replace(/^\s+|\s+$/g,'');
}

/*
   Check if a string is in valid email format.
*/
function isEmail(str)
{
var regex = /^[-_.a-z0-9]+@(([-a-z0-9]+\.)+(ad|ae|aero|af|ag|
ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|
bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|
ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|
ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|
gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|
il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|
kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mil|mk|
ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|
ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|
pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|
si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|
tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|
vu|wf|ws|ye|yt|yu|za|zm|zw)|(([0-9][0-9]?|[0-1][0-9][0-9]|[2]
[0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2]
[0-4][0-9]|[2][5][0-5]))$/i;
return regex.test(str);
}

